1. Field of the Invention
The present invention relates to an organic-inorganic hybrid material for use in electron devices such as electrophotographic photoreceptors, and more particularly to an electrophotographic photoreceptor including the organic-inorganic hybrid material, a process cartridge using the photoreceptor, an image forming apparatus equipped therewith and an image forming method using the apparatus.
2. Discussion of the Background
Recently, among plastic complex materials, an organic-inorganic hybrid material, wherein an inorganic component is nanoscopically dispersed in organic polymer matrix, attracts attention and is studied to draw an advantage of the in organic component and realize the hybrid synergy. Similarly, a functionalized organic-inorganic hybrid material making use of an advantage of the inorganic material attracts attention as well.
Recently, organic photoreceptors (OPCs) are widely used instead of inorganic photoreceptors for copiers, facsimiles, laser printers and their complex machines because of their good performances and advantages. Specific examples of the reasons include (1) optical properties such as a wide range of light absorbing wavelength and a large amount of absorbing light; (2) electrical properties such as high sensitivity and stable chargeability; (3) choice of the materials; (4) good manufacturability; (5) low cost; (6) non-toxicity, etc.
In these circumstances, as image forming apparatuses are being downsized, photoreceptors are having smaller diameters. In addition, photoreceptors are required to have high durability as image forming apparatuses produce images at a higher speed and are free from maintenance.
Against this requirement, the organic photoreceptor typically has a soft surface layer mainly formed from a low-molecular-weight charge transport material and an inactive polymer, and therefore the organic photoreceptor typically has a drawback of being mechanically abraded with an image developer and a cleaner with ease when repeated used in the electrophotographic process. In addition, as toner particles has smaller particle diameters due to requirements for high-quality images, cleaning blades need to have higher rubber hardness and higher contact pressure for the purpose of increasing cleanability, and which also accelerates abrading photoreceptors. Such abrasions of photoreceptors deteriorate electrical properties thereof such as sensitivities and chargeabilities, and cause abnormal images such as image density deterioration and background fouling. When a photoreceptor is locally abraded, images having black stripes due to defective cleaning are produced. At present, photoreceptors are exchanged because of these abrasions and damages.
As mentioned above, trials to improve the durability of the organic photoreceptors, i.e., to prolong lives thereof are continued. The lives of the organic photoreceptors have been dependent on the electrostatic strength and mechanical strength of the photosensitive layers against scratches caused by papers, cleaning blades and separation picks, etc. contacting the surface thereof. Lately, the electrostatic durability has been improved with selected photoreceptor materials. However, a binder for use in a surface layer of the organic photoreceptor, which is better than polycarbonate, has not been found yet.
Because of these reasons, a need exists for an organic photoreceptor having high durability and less abrasion.
For example, as methods of improving the abrasion resistance of a photoreceptor, (a) Japanese Laid-Open Patent Publication No. 56-48637 discloses a photoreceptor using a hardening binder in its surface layer; (b) Japanese Laid-Open Patent Publication No. 64-1728 discloses a photoreceptor using charge transport polymer material; and (c) Japanese Laid-Open Patent Publications Nos. 4-281461, 61-132954, 2-240655, 7-26140, 5-306335, 6-32884 and 6-282094 disclose a photoreceptor having a surface layer wherein an inorganic filler is dispersed.
In addition, Japanese Laid-Open Patent Publications Nos. 56-117245, 63-91666 and 1-205171 disclose a method of improving the mechanical strength by including particulate silica in the surface layer of a photoreceptor. In addition, Japanese Laid-Open Patent Publications Nos. 57-176057, 61-117558 and 3-155558 disclose a method of including a hydrophobic particulate silica in the outermost layer of a photoreceptor, which is the particulate silica surface-treated with a silane coupling agent, etc., to enlarge the mechanical strength thereof and impart lubricity thereto such that the photoreceptor has high durability.
In addition, Japanese Laid-Open Patent Publication No. 2000-105474 discloses a method of hydrolyzing and polycondensating alkoxysilane under the presence of a polycarbonate resin to improve the abrasion and damage resistance of a photoreceptor.
Further, Japanese Laid-Open Patent Publication No. 2002-241483 discloses a method of preparing an organic-inorganic hybrid polymer material, i.e., terminally silyl-modified polycarbonate. In addition, Japanese Laid-Open Patent Publication No. 11-209596 discloses a method of preparing an organic-inorganic hybrid material by hydrolyzing and polycondensating a polymer having polycarbonate and/or polyarylate as a main skeleton and a metal alkoxide group as a functional group.
In addition, Japanese Patent No. 3368415 and Japanese Laid-Open Patent Publication No. 2003-98710 disclose a method of preparing an electrophotographic photoreceptor comprising an electroconductive substrate and a photosensitive layer thereon, wherein an outermost layer thereof comprises a charge transport polymer material, an inorganic filler and particulate acrylic modified polyorganosiloxane, and wherein an aromatic polycarbonate resin synthesized from charge transportable diol is used as the charge transport polymer material.